1. Field of the Invention
This invention relates to a new process for the direct catalytic hydrogenation of butterfat without preliminary separation of short-chain fatty acids using particulate and/or granulated catalysts containing copper chromite.
2. Statement of Related Art
Fatty alcohols, which are predominantly linear, monofunctional alcohols having chain lengths of 8 or more carbon atoms, and their production are described in detail in the literature (Ullmanns Encyklopadie der technischen Chemie, 4th Edition, Vol. 11, pages 427 to 445). A preferred starting material for their production are the fatty acids and fatty acid mixtures occurring in natural fats and/or oils which may be converted into fatty alcohols of corresponding chain length by catalytic hydrogenation. Through the use of the methyl esters of the fatty acids rather than the free fatty acids, themselves, the catalysts are protected against aggressive attack by the free carboxyl group. This enables industrial processes to be operated for sufficiently long periods with satisfactory volume-time yields. Today, therefore, the predominant quantity of native fatty alcohols is produced from fatty acid methyl esters by the gas-phase hydrogenation process in which the distilled methyl esters are passed in the vapor phase together with a large excess of hydrogen over a fixed bed of copper-containing mixed oxide catalysts such as, for example, copper chromite spinel catalysts. Temperatures above 200.degree. C. and under pressures of from about 250 to 300 bar are useful.
Copper-mixed oxide catalysts obtained by co-precipitation via the wet route are used as particulate catalysts or extrudates. Before use the catalysts are generally reduced in the plant or installation.
Fatty acid esters, especially fatty acid methyl esters, and free fatty acids are used simultaneously as starting materials for the hydrogenation reaction to saturated and/or unsaturated fatty alcohols according to the patent literature, for example, U.S. Pat. Nos. 3,193,586, 3,173,959, and German Patent Nos. 2,513,377 and 2,613,226.
By virture of its fatty acid composition, butter is a tallow substitute. By melting out butter, separating off the aqueous phase and heating to 100.degree. to 105.degree. C., it is possible to obtain clarified or run butter which is 99.3% butterfat containing at most 0.5% water and hardly any lactose, casein or salts (Rompp's Chemie Lexikon, 8th Edition, page 544. Butterfat is defined in the prior art as the oily portion of mammals milk composed of 88% of the glycerides of oleic, stearic, and palmitic acids, and 6% of the glycerides of butyric, caproic, caprylic and capric acids (HACKH's Chemical Dictionary, 4th Edition, page 117).
In the conventional processing of butter or butterfat, process-related difficulties are encountered both during the transesterification step and during the fat splitting step on account of the high proportion of short-chain fatty acids containing from 4 to 10 carbon atoms. These difficulties lead to uneconomical hydrogenation processes. The short-chain fatty acids are normally separated off as methyl esters. In this case, just as in processing by fat splitting, unpleasant odors are emitted by the short-chain fatty acids. In addition the high solubility of the fatty acids in the water of the splitting reaction presents practical problems.
Further problems arise in the separation of the methanol from the short-chain fatty acids because the boiling points partly overlap so that some of the methanol is lost during working up.
Co-pending application U.S.S.N. 074,814, filed July 17, 1987, describes subject matter which is related to the present invention.